Course Schedule

#include <iostream>
#include <stack>
#include <vector>
using namespace std;

stack<int> sort;
vector<vector<int>> adj;
vector<int> state;

bool dfs(int node) {
    if (state[node] == 2) return true;
    if (state[node] == 1) return false;
    state[node] = 1;
    for (auto v: adj[node]) {
        bool res = dfs(v);
        if (!res) return false;
    }
    sort.push(node);
    state[node] = 2;
    return true;
}

int main() {
    int n, m;
    cin >> n >> m;
    adj.resize(n);
    state.resize(n);
    for (int i=0; i<n; i++) { state[i] = 0; }
    for (int i=0; i<n; i++) { adj[i] = vector<int>(0); }

    int a, b;
    for (int i=0; i<m; i++) {
        cin >> a >> b;
        a--; b--;
        adj[a].push_back(b);
    }

    for (int i=0; i<n; i++) {
        bool res = dfs(i);
        if (!res) {
            cout << "IMPOSSIBLE" << endl;
            return 0;
        }
    }

    cout << sort.top()+1;
    sort.pop();
    while (!sort.empty()) {
        cout << " " << sort.top()+1;
        sort.pop();
    }
    cout << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED